Difference between Voltage and Current

[ronaldrc]

If any Moderator thinks this might stir up to much controversy please remove it and I will
understand and have no hard feelings. This is just my personnel opinion. Thanks



What is Voltage and what is current and what are the differences.

I am not posting this to mislead any ones beliefs and if it does, Please let me apologize in advance.

I'm not an Engineer nor instructor so please take these statements with a grain of salt but please read
and think about them.


Theories of the direction of the flow of electrical current.


In the study of Electricity I like to use the analogy of water flowing through pipes from the source in this case the pump to the load, water wheel Etc, to do our work then collected and sent back to the pump again in a continuous cycle. And if AC it alternates.

Below are the 2 most popular beliefs of the direction of current flow.

(1)-Electron Flow Positive or + Pulls and Negative or – Pushes.
(2)-Conventional Flow Negative or -Pulls and Positive or + Pushes.


Either direction works with most active circuit elements as long as you stay consistent through your circuit when studying the Effects it has on your loads and voltage sources on one another.


I like to apply the Electron flow when studying the direction of flow of a current in a wire simply because of the theory behind the fleming valve invented by Ambrose Fleming which became known as the Electron vacuum tube. In this theory the electrons flow from the cathode to the anode or from the filament to the plate. It would be hard to imagine that they flow from the anode or plate to the cathode or filament since we use the term the filament boils the electrons off and are pulled to the plate by a B+ voltage or a positive voltage. The Fleming valve implies that the positive or the + terminal of a electrical voltage source pulls and the Negative pushes.


Theories of how the current flows.

On this subject almost no one agrees you hear everything from AC doesn't flow continuously
through the circuit reverses and back again. It flow just a little bit maybe a thousandths of an inch to a meter or so and the back ,or just wiggles around a bit.


As far as that goes DC might flow in both directions, in one direction it produces work which we can see use and measure and in the other direction it does not produce any work that we can use or measure with the instrument we now have.

No one knows the answers to these questions yet.



But until we do why not use the water flow analogy it works almost perfect when we apply the electrical formulas we have.



What is voltage and what is current.


First I have always had a problem with the way text books and folks in the Electrical field refer
to voltage as a physical thing that flows through conductors or wires.


The definition of voltage is the force behind an electrical current or the potential between the
two points of an Electrical source. It is an expression or an entity that pushes the current through
the conductors or wires. According to that definition it is not a physical thing that flows through the wires with the current.

Like a water pump that pumps the water, the water pump itself does not flow through the water pipe the water flows through the pipe and the pump forces it through by putting more water behind the water with a mechanical force.



Effect of Inductive kickback or Power factor and capacitance on the Electrical current flow through conductors.

When you study Electrical current flow you hear the statements about the current lagging behind or leading the voltage because of the effect of Induction and capacitance. Am I the only one that has a problem with this?


I don't think the original author was insinuating this but when I read this I see a separate physical thing as the voltage which flows right along with the current, when in fact he meant the pressure or force of the voltage source.


The definition of voltage is the force or potential difference between the poles of a voltage source.

How can the voltage lead or lag if it is just the force that the source produces? It is a entity not nothing physical thing running through the conductors.

When you watch a sine wave on a dual trace scope and and put a inductor in series with your load you will see another sine wave behind the original one.

Belief is this is the current lagging behind the voltage. But isn't it really another current generated by the original current lagging behind the original first one produced? Like the water pump forcing more water into pipe, this would be the battery or generator forcing more electrons into the wire thereby pushing the other electron farther through the wire. You could call this apparent voltage I guess:roll:

Remember voltage is merely the force driving the current through the wire not something traveling around the circuit with it.

And I think the same theory could be applied to Capacitance.

I'm sure you all will straighten me on these beliefs.

Thanks for reading
Please give me your thoughts on this. :Ronald

 

[kwired]

I like to think of current as more like a line of billiard balls in a line butted against one another. Hit the end of the line with another ball and the energy is pushed through the line but does not move the balls until it hits the end of the line and the last ball moves. Difference with an electrical circuit is there is no end to the line but energy is still imposed on it and moves through the conductor. Open the circut and that energy is still available but has no place to go. No material in the conductor actually moves, the electrons just bump against the adjacent electrons just like the billiard balls bump up against the adjacent ball transferring the energy to the next one. The electrons in an insulating material are not easily "bumped" by the energy in the electrons of the conductive material.

 

[ronaldrc]

Thats not really that different from the water analogy.

I'm inclined to agree about the particles in the copper not really moving.

We understand less about magnetic energy than we do gravity.

I think all the energy is in the magnetic waves around the wire.
But then again you do have to make a physical contact with the wires
to produce a large current flow. :?

Ronald

 

[rattus]

Thats not really that different from the water analogy.

I'm inclined to agree about the particles in the copper not really moving.

We understand less about magnetic energy than we do gravity.

I think all the energy is in the magnetic waves around the wire.
But then again you do have to make a physical contact with the wires
to produce a large current flow. :?

Ronald

I believe carriers (electrons) really do flow, but since their density is so high in copper, they don't have to move very fast to create a current.

 

[gar]

111124-2022 EST

ronaldrc:

The conventions "electron flow" and "positive current flow" are just two ways of assigning a direction for descriptive purposes.

"Electron flow" is actually based on the direction of flow of electrons in an electron tube. Individual electrons do actually flow from cathode to anode, and an individual electron has a transit time based on the distance from cathode to anode, its mass, initial velocity, and accelerating electric field. If the negative voltage of the grid in a triode vacuum tube is sufficiently negative, maybe -12 V for the grid voltage at a plate voltage of 300 V for cutoff of a 6J6, and -4 V at 100 V, then no current flows. At cutoff and below there is simply a space charge of electrons boiling off the cathode and returning to it.

"Positive current flow" is nothing but a convention that has been around for a very long time and is used by electrical engineers for most circuit analysis, including external circuits with vacuum tubes.

On the question of leading and lagging, just view these as descriptive names. They are just a means of describing how one sine wave appears in relation to another.

Consider a capacitor with a sine wave voltage applied across the capacitor. I do not care how you get the sine wave voltage across the capacitor, it is just there.

The equation that relates voltage and charge for a capacitor is

q = C * v

Current is the rate of change of charge with respect to time. In other words how fast charge moves is current. Current is higher as charge moves faster. Thus,

i = dq/dt or the integral of i with respect to t is q. In other words adding up all the small elements of current in each small element of time equals the total change in charge.

i = d(C*v)/dt or C * dv/dt

dv/dt is the rate of change of voltage with respect to time.

In calculus you learn how to derive various differentials and integrals.

It turns out that dv/dt of v =V*sin t = V*cos t * dt/dt = V*cos t

So if v = V*sin t, the voltage across the capacitor, then i = C * V * cos t, the current flow to the capacitor. This is obviously for steady state conditions of a continuous sine wave. When v = 0, i = its maximum positive value, and when v is at its maximum positive value, then i = 0. Since the cos wave is positive before the voltage is positive as time increases this is described as the current leading the voltage.

.

 

[Little Bill]

So what did you guys think of the Cowboys vs Dolphins game? Dolphins were one electron short I believe!:lol:

 

[ronaldrc]

I believe carriers (electrons) really do flow, but since their density is so high in copper, they don't have to move very fast to create a current.

I probably really agree with you on that. Thats what my remark was made for at the end of my post.

About the contact of the two conductors for a large current to flow.Or flipping a switch to complete the circuit.

Ronald

 

[ronaldrc]

111124-2022 EST

"Positive current flow" is nothing but a convention that has been around for a very long time and is used by electrical engineers for most circuit analysis, including external circuits with vacuum tubes.

.

Gar: My memory is rusty on Vacuum tube electronics but if I remember right you bias a vacuum tubes control grid with a positive voltage to bring half way up to B+ power level.That way you can duplicate any input signals swing from negative to positive.

I understand what you are saying about putting a -12 volts on the grid to completely cut the flow off from the plate.


When you mentioned convention above I'm sure you meant conventional flow. I would have a hard time analizing
any kind of electronic circuits using conventional flow. Even the pnp and npn transistors symbols are setup to use
Electron flow or at least they seem to be to me. Now let me tell you right now I was wrong once before. :roll:

Thanks for the replies: Ronald

 

[ronaldrc]

So what did you guys think of the Cowboys vs Dolphins game? Dolphins were one electron short I believe!:lol:

Who won I fell to sleep after eating all that Turkey, oh well better than crowe I guess.

 

[gar]

111124-2329 EST

ronaldrc:

Think about the grid. If it becomes positive relative to the cathode, it will be just like the anode of a diode, except it will lack the surface area of the anode and can not dissipate much heat. Under normal operating conditions you operate with the grid always negative, and stay away from close to 0 V, at least for linear applications.

Squaring (like square wave or binary) or clipping circuits would drive the grid from below cutoff to a voltage toward greater than zero, but clamp at 0 with a diode or adequate series resistance to the grid to limit current.

No matter what the devices are used in a circuit electrical engineers use the "positive current" convention for analysis of the circuit.

Convention as used means common agreement.

From dictionary.com

con?ven?tion   /kənˈvɛnʃən/ Show Spelled[kuhn-ven-shuhn] Show IPA
noun
1. a meeting or formal assembly, as of representatives or delegates, for discussion of and action on particular matters of common concern.
2. U.S. Politics . a representative party assembly to nominate candidates and adopt platforms and party rules.
3. an agreement, compact, or contract.
4. an international agreement, especially one dealing with a specific matter, as postal service or copyright.
5. a rule, method, or practice established by usage; custom: the convention of showing north at the top of a map.

.

 

[Little Bill]

Who won I fell to sleep after eating all that Turkey, oh well better than crowe I guess.

Cowboys 20-19

I really was just being silly as I had nothing to add to your thread. Even if I did, I'm turkey brain dead too.

 

[ronaldrc]

111124-2329 EST

ronaldrc:

Think about the grid. If it becomes positive relative to the cathode, it will be just like the anode of a diode, except it will lack the surface area of the anode and can not dissipate much heat. Under normal operating conditions you operate with the grid always negative, and stay away from close to 0 V, at least for linear applications.

Squaring (like square wave or binary) or clipping circuits would drive the grid from below cutoff to a voltage toward greater than zero, but clamp at 0 with a diode or adequate series resistance to the grid to limit current.

No matter what the devices are used in a circuit electrical engineers use the "positive current" convention for analysis of the circuit.

Convention as used means common agreement.

From dictionary.com


.

You're right my bad, The conduction between the cathode and anode are already in full conduction so we have to make the gid more nagitive than the cathode to bring the B+ power supply down to aprox. 50 percent to allow for a swing in either direction for linear amplication.

I told you I was rusty on that subject.

Thanks

 

[gar]

111125-0859 EST

rolandrc:

No problem it is easy to have the mind shift things around over time.

If you are interested in some of the theory of electron tubes a good book is
"Fundamentals of Engineering Electronics", by William G. Dow, 1952, John Wiley & Sons.
According to Google there are 335 libraries where this book can be found.

A test question we had was:
A square box with a hole in one side with an electron entering perpendicular to the wall at some initial velocity. Within the box was a uniform electric field, and a uniform magnetic field. Adjust these fields (determine their values) to make the electron exit the box on the opposite side of the box at a location displaced from being in line with the entry point. Actual dimensional positions were provided.

In the first chapter of Dow's book "Space-Charge Control of Plate Current by Grid and Plate Voltages." is discussed.

Another good book in this area is "Electronics", by Milllman and Seely, 1951, McGraw-Hill.

I suspect that many readers here have never built an electron tube circuit, or maybe even a transistor circuit. These are fun for experimentation. One of the ideas developed early in electronic circuits with vacuum tubes for digital circuits was to drive the grid from below cutoff toward a much higher positive voltage than 0, but then clamp at 0. This was to reduce the switching delay time resulting from the input capacitance of the grid circuit.

One of the annoying parts of making a tube circuit was the need to provide heater or filament voltage. Also the warm up time.

.

 

[Besoeker]

Effect of Inductive kickback or Power factor and capacitance on the Electrical current flow through conductors.

When you study Electrical current flow you hear the statements about the current lagging behind or leading the voltage because of the effect of Induction and capacitance. Am I the only one that has a problem with this?

Inductors and Capacitors can store energy.
¹/₂*L*I² and ¹/²*C*V² respectively.
Energy is the product of power and time - Watt seconds (Joules) for example or kWh that your bill is calculated from.

Stick with the inductor for now. You can't go from zero energy to some finite value instantly - that would infer infinite power. Some Watt seconds in no seconds so infinite Watts.
If you connected a voltage V across an inductor L, the current would rise at a rate V/L, building up the energy stored in the inductor.
It would continue but practicalities mean that the circuit will have some resistance and that limits the steady state current.
In short, the current must lag the voltage as a consequence of the energy storage.

 

[charlie b]

In the study of Electricity I like to use the analogy of water flowing through pipes from the source in this case the pump to the load

That analogy has some value. There are ways in which it works well. For example,

• The units of measure for flow are similar, both representing “amount of stuff per unit time.” For pipes, it is gallons of fluid per minute, and for wires it is (essentially, though not precisely) numbers of electrons per second.
• The flow at the start of a long pipe (or wire) will be the same as the flow at the end of the pipe (or wire).
• The larger the pipe (or wire), the more flow it can carry.
• The pressure (voltage) at the end of a pipe (wire) will be lower than at the beginning, due to pressure drop (voltage drop) along the pipe (wire).

There are also some ways in which that analogy falls short. For example,

• The units of measure for pressure and voltage are nothing at all like each other. Pressure is measured in pounds of force per unit area. I’ll get to voltage later.
• If you knew the flow rate of water passing a point along the pipe, in units of gallons per minute, that would not be enough information for you to calculate the number of water molecules passing that point, because you also need to take density of water into account. Electrical current does not have an analogy to density.
• Looking in cross-section, the flow of water is fastest in the center of the pipe, and the water velocity approaches zero as you get closer to the pipe’s inner wall. Electrical current, by contrast, flows mostly along the outside of the wire, and flow is zero in the center of the wire.
• There is no electrical analogy to the effect of turbulent flow in a pipe.
• There is no mechanical analogy to the storage of energy in, and exchange of energy between, magnetic fields (i.e., inductors) and electric fields (i.e., capacitors).

On this subject almost no one agrees you hear everything from AC doesn't flow continuously through the circuit reverses and back again. It . . . just wiggles around a bit.

True, but irrelevant. Current is actually defined as “charge in motion.” The fact that electrons within a copper wire have a negative charge is what enables the motion of electrons to comprise current. Although the notion of electrons “wiggling back and forth” is a more accurate description of what happens inside a copper wire, I believe it is an acceptable practice to visualize electrons (billions of billions at a time) actually moving down the wire at nearly the speed of light. From the perspective of an observer standing outside the wire (or from the perspective of the clamp-on ammeter surrounding the wire), what is being observed (or measured) is an amount of charge moving past your location in a given period of time.

No one knows the answers to these questions yet.

Yes we do. The physics of electrical current has been well understood for over a century, and it is what is taught in electrical engineering degree programs.

The definition of voltage is the force behind an electrical current or the potential between the two points of an Electrical source. It is an expression or an entity that pushes the current through the conductors or wires.

I must report, with respect, that here you have it completely wrong. Although the “water analogy” would have you thinking of voltage as the “driving force” for electron flow, voltage is absolutely not about “force.” The definition of voltage is the amount of energy required to move an amount of charge from one location to another. The unit of measure called “one volt” is defined as “one joule (of energy) per coulomb (of charge).” As I said earlier, this is not at all similar to the unit of measure for pressure.

When you study Electrical current flow you hear the statements about the current lagging behind or leading the voltage because of the effect of Induction and capacitance. Am I the only one that has a problem with this?

You are not likely to be the only one, but I for one do not have a problem with it. Voltage can be displayed on an oscilloscope or on a sheet of paper, and its waveform will look like any sine wave. You can display the current on the same o-scope or sheet of paper, and it too will look like a sine wave. But you should be careful to let the viewer know that the two sine waves use a different scale and have different units of measure, and that you are showing them together merely for the sake of convenience. Taking a purely inductive circuit as an example, the combined display will show the voltage reaching its positive or negative peak at specific points in time, and it will show the current reaching its peaks a short time (specifically, one quarter of the cycle) later. In an inductor, the voltage leads the current by 90 degrees, which is the same as saying the current lags the voltage by 90 degrees.

How can the voltage lead or lag if it is just the force that the source produces? It is an entity not nothing physical thing running through the conductors.

Here again, voltage is not a “force,” and it is indeed a physical phenomenon. The separation (in time) between current and voltage does not take place at the source. It is a result of a physical event taking place in the inductor (or capacitor). It happens at different times than the current specifically because of what happens inside the inductor (or capacitor). For example, when you try to push current through a coil of wire (i.e., an inductor), the coil will create across itself a voltage that tends to oppose the flow of current. Sometime later, current will have succeeded in making its way through the inductor. But having to fight the voltage source created by the inductor itself will have caused a delay in the current. That is why the two sine waves do not lay one on top of the other, and why the current lags the voltage.

 

[ggunn]

As a musician, one of my biggest disappointments in the EE program where I studied was that no courses on electron tubes were offered. Tube amps rule!

 

[Stevareno]

http://forums.mikeholt.com/showthread.php?p=1352484#post1352484

When you study Electrical current flow you hear the statements about the current lagging behind or leading the voltage because of the effect of Induction and capacitance. Am I the only one that has a problem with this?

I don't. I think of leading/lagging as just a reference statement that describes what happens to the current (as referenced from the source) when it passes through an inductor/capacitor.

 

[ronaldrc]

I do appreciate all the input from everyone.

What I said about voltage being equal to pressure and difference in potential between two points and not a separate entity running alone with the current in the conductor as of right now ,I still believe what I said.

Some or all my opinions might change later. But for right now none have changed.

I am always open for different opinions, and when I see they are wrong I will own up to it. I don't mind in the least to eat crow.

Charlie makes a very good argument and its hard not to agree with him.

The opinions I give are my own, I don't expect anyone to agree with them, all I ask is for you to think about them
and give me your honest opinion.

The way Charlie explained it the voltage is a separate material thing that flows in the conductor and governs what the current does. I am very skeptical about that.

Ronald

 

[Besoeker]

Good post, Charlie B. I'll address just a couple of points.

There are also some ways in which that analogy falls short. For example,

The units of measure for pressure and voltage are nothing at all like each other. Pressure is measured in pounds of force per unit area. I?ll get to voltage later.

I think the analogy actually holds reasonably well for this. Increase the pressure and the flow will increase in the pipe, all other things being equal. Increase the voltage applied to an electrical and more current will flow.

Looking in cross-section, the flow of water is fastest in the center of the pipe, and the water velocity approaches zero as you get closer to the pipe?s inner wall. Electrical current, by contrast, flows mostly along the outside of the wire, and flow is zero in the center of the wire.

I agree. They are not analogous. But, if you have sufficient knowledge to understand laminar flow and skin effect, you are probably past the stage where you need such analogies to aid your understanding.

There is no mechanical analogy to the storage of energy in, and exchange of energy between, magnetic fields (i.e., inductors) and electric fields (i.e., capacitors).

I can think of a few but just take a simple pendulum. In operation it exchanges energy between PE and KE. At the end of its travel, it has just potential energy. At the mid point, it has just kinetic energy. It has a defined oscillation period. Just like the exchange of energy between a capacitor and an inductor. The analogy goes further. Without further energy input, both would cease to oscillate after a time and both for the same fundamental reason. Losses.

 

[Besoeker]

As a musician, one of my biggest disappointments in the EE program where I studied was that no courses on electron tubes were offered. Tube amps rule!

I was going to ask if you can still buy tubes but I just check what is offered by one of the largest distributors here and they do offer a selection.
Out of 18,000 products offered, 13 are tubes (thermionic valves)
And very expensive.
I'm sufficiently ancient to have learned about them but the nearest I got to that kind of thing was thyratrons for DC motor control (which we replaced with SCRs) and a few mercury arc rectifiers which we also replaced.